Stefan Hild

January 2009

Pick-off beams in the central Interferometer of Advanced Virgo

S. Hild January 2009 Slide 2

Creation points of Pick-off beam

All Anti-reflex coatings potentially cause secondary beams.

Pick-off beams have about 10 to 20mW (6ppm x 2.7kW)

Pick-off beams are of similar size as the main IFO beam (LARGE!)

These 15 (18) beams should either be detected or properly dumped

3 beams from PRC(+3 beams from SRC) 2 beams

4 beams

2 beams

4 beams

S. Hild January 2009 Slide 3

Why more pick-off beams than in Virgo?

Pick-off port Initial Virgo Advanced Virgo

Input mirror AR Etalon 2 beams each

Compensation plates No CPs 4 beams each

BSAR PRC 1x used (B5)

2x unused (not dumped)

3 beams

BSAR SRC 3x unused

(not dumped)

(3 beams ?)

S. Hild January 2009 Slide 4

Input mirror AR coating

Can an Etalon (A) be control-led well enough with the CP so close by?

C should be avoided, because of scattered light.

D: one beam is strongly divergent.

S. Hild January 2009 Slide 5

Pick-offs from the CPs

CP is probably primary pick-off for ISC.

For ASC it might be important to have no overlapping beams (distributing the secondary beams in 3D).

Divergence of CP pick-offs depends on IM backsurface (lens or not).

If we get the CP pick-offs to work for ISC, we can probably dump the B5 beam.

S. Hild January 2009 Slide 6

Secondary reflections from BS 3 beams from within PRC needs

to be dealt with for AdV.

What to do about the 3 beams from within the SRC (in contrast they are not differential)?

Do we need B5 or can it be dumped?

Currently not dumped beam